6（x-y)-7(xy)=21,2(x-y)-5(x+y)=-1

6（x-y)-7(xy)=21,2(x-y)-5(x+y)=-1 已知X+y=6,xy=7 求x^2y+xy^2=已知X+y=6,xy=7 x^2y+xy^2 已知1/x-1/y=2,求3x+7xy-3y/2x-3xy-2y答案是1/x-1/y=2(y-x)/xy=2 得：x-y=-2xy(3x+7xy-3y)/(2x-3xy-2y)=[3(x-y)+7xy]/[2(x-y)-3xy]=(-6xy+7xy)/(-4xy-3xy)=xy/(-7xy)=-1/7 谁能帮我解释一下=[3(x-y)+7xy]/[2(x-y)-3xy]=(-6xy+7xy)/(-4xy-3xy) 是怎 化简求值x-4y/2x-7xy+3y×x-2xy-3y/2x+3xy-2y÷3x-6y/4x-4xy+y,其中：x=1999,y=-1 1、(-7x^y)(2x^y-3xy^3+xy) 2、((x-y)^6)/((y-x)^3)/(x-y) x+y=8,xy=-2,求(5xy+4x+7y)+(6x-3xy)-(4xy-3y)的值 3/x —2/y=3 (2x-3y-xy) / (7xy+9y-6x)= 已知1/x - 1/y = 2,求3x+7xy-3y / 2x-3xy-2y的值1/x-1/y=2(y-x)/xy=2 得：x-y=-2xy(3x+7xy-3y)/(2x-3xy-2y)=[3(x-y)+7xy]/[2(x-y)-3xy]=(-6xy+7xy)/(-4xy-3xy)=xy/(-7xy)=-1/71/x-1/y=2到(y-x)/xy=2 是怎么变化的.. 1-2/x+y=xy,4y+6x=xy.求xy的解? 先化简,再求值：-4x+7x-5-3x-6x+2,其中x=-2分之1 4xy-3x-xy先化简,再求值：-4x+7x-5-3x-6x+2,其中x=-2分之14xy-3x-xy+y+x-3xy-2y+2x+x,其中x=-5,y=-1 x^2-xy-2y^2+x+7y-6 x²+xy-2y²-x+7y-6 2x^+xy-y^-4x+5y-6=? 已知x-xy =21,xy-y=-12,分别求式子x-y与x-2xy +y 已知xy/x+y=3,则代数式2x-7xy+2y/-x+xy-y的值是多少? 诺x+y=6,xy=4 求(5x-4y-3xy)-(8x-y+2xy) 已知xy/x+y=6,求3x-2xy+3y/-x+3xy-y的值. 已知(xy)/(x+y)=6求(3x-2xy+3y)/(-x+3xy-y)的值.